This invention relates to a method of writing servo data on a magnetic disk medium such as a large-capacity flexible or floppy disk by a magnetic head and a servo writer for the large-capacity flexible or floppy disk.
As is well known in the art, a flexible or floppy disk drive (which may be abbreviated to "FDD") is a device for carrying out data recording and reproducing operations to and from a magnetic disk medium such as a flexible or floppy disk (which may be abbreviated to "FD") inserted therein. In recent years, FDs have been more and more improved to have a greater capacity. Specifically, development has been made of FDs having a storage capacity of 128 Mbytes (which may be called large-capacity FDs) in contrast with FDs having a storage capacity of 1 Mbyte or 2 Mbytes (which may be called small-capacity FDs). Following such development, the FDDs have also improved to accept the large-capacity FDs for data recording and reproducing operations to and from the magnetic disk media of the large-capacity FDs.
Throughout the present specification, FDDs capable of recording/reproducing data for magnetic disk media of the large-capacity FDs alone will be referred to as high-density exclusive type FDDs. On the other hand, FDDs capable of recording/reproducing data for magnetic disk media of the small-capacity FDs alone will be called low-density exclusive type FDDs. Furthermore, FDDs capable of recording/reproducing data for magnetic disk media of both the large-capacity and the small-capacity FDs will be called high-density/low-density compatible type FDDs. In addition, the high-density exclusive type FDDs and the high-density/low-density compatible type FDDs will collectively be called high-density type FDDs.
The low-density exclusive type FDD and the high-density type FDD are different in mechanism from each other in several respects, one of which will presently be described. In either FDD, a magnetic head is supported by a head carriage which is driven by a drive arrangement to move in a predetermined radial direction with respect to the magnetic disk medium of the FD inserted in the FDD. The difference resides in the structure of the drive arrangement. More specifically, the low-density exclusive type FDD uses a stepping motor as the drive arrangement. On the other hand, the high-density type FDD uses a linear motor such as a voice coil motor (which may be abbreviated to "VCM") as the drive arrangement.
Now, description will be made of the voice coil motor used as the drive arrangement in the high-density type FDD. The voice coil motor comprises a voice coil and a magnetic circuit. The voice coil is disposed on the head carriage at a rear side and is wound around a drive axis extending in parallel to the predetermined radial direction. The magnetic circuit generates a magnetic field in a direction intersecting that of an electric current flowing through the voice coil. With this structure, by causing the electric current to flow through the voice coil in a direction intersecting that of the magnetic field generated by the magnetic circuit, a drive force occurs in a direction extending to the drive axis on the basis of interaction of the electric current with the magnetic field. The drive force causes the voice coil motor to move the head carriage in the predetermined radial direction. Throughout the present specification, the head carriage driven linearly by such a linear motor will be called a direct-acting head carriage.
In the meanwhile, the large-capacity FD generally has an external configuration which is substantially identical with that of the small-capacity FD. Specifically, both of the large-capacity and the small-capacity FDs have a flat rectangular shape with a width of 90 mm, a length of 94 mm, and a thickness of 3.3 mm in the case of a 3.5-inch type FD. As is well known in the art, the FD comprises a disk-shaped magnetic disk medium covered with a case which is called a shell. The case consists of an upper case and a lower case with the magnetic disk medium sandwiched therebetween. The upper and the lower cases have upper and lower openings, respectively. The magnetic disk medium of the FD is accessed by upper and lower magnetic heads via the upper and the lower openings. The magnetic disk medium of the FD has both sides on which a plurality of tracks are concentrically disposed along a radial direction. The magnetic disk medium of the large-capacity FD has a track width (track pitch) which is narrower than that of the magnetic disk medium of the small-capacity FD. Inasmuch as the magnetic disk medium of the large-capacity FD has a narrower track width (track pitch), servo data for position detection is preliminarily written on the magnetic disk medium of the small-capacity FD.
As is well known in the art, the small-capacity FD is sold in two forms as follows. In a first form, the small-capacity FD is sold with an unformatted, unitialized disk medium. In a second form, the small-capacity FD is sold with a formatted disk medium whereby an unformatted disk medium is formatted by a formatter. On buying the small-capacity FD with the unformatted disk medium, a user carries out writing/reading of data in/from the magnetic disk medium after the unformatted disk medium is initialized or formatted. On the other hand, on buying the small-capacity FD with the formatted disk medium, a user can immediately carry out writing/reading of data in/from the magnetic disk medium without initialization or formatting.
In contrast with this, the large-capacity FD is sold in two forms as follows. In a first forms, the large-capacity FD is sold with a servo-formatted disk medium whereby an unformatted disk medium is servo-formatted by a servo writer (or servo data is written in the unformatted disk medium). In a second form, the large-capacity FD is sold with a data-formatted disk medium whereby the servo-formatted disk medium is data-formatted by a formatter. On buying the large-capacity FD with the servo-formatted disk medium, a user carries out writing/reading of data in/from the magnetic disk medium after the servo-formatted disk medium is data-formatted by the formatter. On the other hand, on buying the large-capacity FD with the data-formatted disk medium, a user can immediately carry out writing/reading of data in/from the magnetic disk medium without data-formatting. In servo-format using the servo writer, the servo writer constructs the tracks on the unformatted disk medium at a track pitch of about 10 .mu.m, partitions each track into a plurality of sectors, and writes position information for the tracks and the sectors on the magnetic disk medium. The servo writer may be called a servo track writer.
In order to write the servo data on the unformatted disk medium of the large-capacity FD, a conventional servo writer uses, as a drive mechanism, a head carriage into which a head gimbal assembly (HGA) used in a hard disk drive (HDD) is modified and writes the serve data on the magnetic disk medium by the magnetic head with a load/unload mechanism for the magnetic head set outside. The unformatted disk medium is rotatably supported by a spindle via an air bearing. The conventional servo writer can directly write the servo data on the unformatted disk medium without the case (shell).
As is well known in the art, in the hard disk drive, the magnetic head is supported by a supporting spring (load arm) in a suspension fashion. The magnetic head consists of a core for recording information on a hard magnetic disk medium of a hard disk and a slider for having the core surface with an extremely narrow gap (which is called a spacing) left between the hard magnetic disk medium and the core. Such a magnetic head is called a monolithic head. In the hard disk drive, it is not presumed that a recording medium moves up and down on rotating of the recording medium. This is because the hard magnetic disk medium is used as the recording medium for the hard disk drive.
It is assumed that the recording medium presents flexiblity like the flexible magnetic disk medium of the flexible disk. In the above-mentioned supporting structure (the head gimbal assembly) for magnetic heads in the hard disk drive, a position of a pair of upper and lower magnetic heads shifts from a desired track position on the recording medium. In other words, in a case where the head carriage for the servo writer is one into which the head gimbal assembly used in the hard disk drive is modified, it is very difficult to select and adjust the magnetic heads because of adverse effect of balance of the pair of upper and lower magnetic heads. A yield factor in the magnetic head is degraded and the magnetic head becomes expensive. When a load of the head gimbal assembly is not balanced, modulation occurs due to corrugation of the flexible magnetic disk medium. As a result, it is impossible to write the servo data on the flexible magnetic disk medium.
Furthermore, inasmuch as the head gimbal assembly is particularly processed to enable loading and unloading, the rigidity of a connection rod for mounting the head gimbal assembly must be improved and this results in degraded mechanical characteristics of the serve writer from the point of view of mass.